linux-kernel - Re: Full dynticks needs evtdesc set before marking cpu online.

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Date:	Mon, 13 May 2013 16:04:45 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Robin Holt <holt@....com>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: Full dynticks needs evtdesc set before marking cpu online.

On Mon, 13 May 2013, Robin Holt wrote:
> On Mon, May 13, 2013 at 03:03:55PM +0200, Thomas Gleixner wrote:
> > On Mon, 13 May 2013, Robin Holt wrote:
> > 
> > > On Mon, May 13, 2013 at 11:21:00AM +0200, Thomas Gleixner wrote:
> > > > On Wed, 8 May 2013, Robin Holt wrote:
> > > > 
> > > > > Thomas,
> > > > > 
> > > > > We are seeing failures booting medium sized machines which I think is
> > > > > a change in expectations that dyntick put on x86's start_secondary.
> > > > > 
> > > > > During boot of cpus, we see an occassional panic in tick_do_broadcast at
> > > > 
> > > > http://lkml.indiana.edu/hypermail/linux/kernel/1305.0/01818.html
> > > > 
> > > > Will hit Linus tree soon.
> > > 
> > > I think this is really due to a sequence in start_secondary.  The cpu
> > > has been marked as online, but its evtdesc has not been initialized.
> > > I sent a followup to this with a hack/patch.
> > 
> > No, the real issue is that I messed up the cpumask conversion in the
> > broadcast code, i.e. using alloc instead of zalloc, which allocated
> > nonzeroed memory for the cpumasks, so any random bit set will crash
> > the machine. Your patch is just papering over the issue.
> 
> I believe I understand now.  What would be the downside of moving
> the initialization to before marking the cpu online?  It seems like a
> reasonable this to expect as well in spite of it not being the right
> fix to the other bug.

Yes, we can move it, but its not a required thing that the tick device
is setup befor onlining.

Thanks,

	tglx
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